This disclosure generally relates to geared turbofan gas turbine engine. More particularly, this disclosure relates to a bearing arrangement supporting rotation of a low spool shaft for a geared turbofan gas turbine engine.
A turbofan gas turbine engine includes a core section and a turbofan section. The core section includes compressor within which air is compressed and forwarded to a combustor where fuel is mixed with air and ignited to generate a stream of high-speed exhaust gases. The exhaust gases flow through a turbine section that extracts power to drive the compressor. The gas turbine engine core can include a low spool and a high spool that can either co-rotate or counter-rotate at different speeds about an axis of the engine. The low spool typically rotates at a lower speed than the high spool and drives the fan. A gearbox can be utilized to provide for the relative rotation of the fan at a different speed than the low spool.
Rotation of the low spool and the high spool is supported by bearing arrangements. Each shaft includes at least one roller bearing and one thrust bearing. The thrust bearing provides both radial and axial support for a rotating shaft. The thrust bearing is typically utilized to maintain a desired axial alignment between relative rotating and stationary elements. However, a thrust bearing requires greater space both radially and axially.
Further, in some engine architectures such as for example a geared turbofan gas turbine engine, the low spool is split into two parts. The low spool that drives a gearbox within the axial space of the compressor section and a second intermediate spool that drives an intermediate compressor. In configurations where the low spool is not split, forward thrust produced by the fan is mostly countered by rearward blow off in the turbine. However, a split low spool configuration cannot take advantage of this balance and a larger thrust bearing is required. Therefore, space within the compressor area is limited. Accordingly, the addition of the gearbox at a forward end of the low spool and/or the use of an intermediate spool reduces the available space within which a bearing arrangement can be supported.